Acceptable risk defined

In use of risk assessment methods, you will find that the methodology for calculating overall risk probabilities is quite well defined. But, assigning realistic values to individual probabilities can be quite difficult, and a matter of personal opinion of the analyst. So, the analyst must have intimate knowledge of the system being evaluated, as well as all effects being considered, before he can make an acceptable risk assessment. 

Risk assessment is the conventional tool for decision making on the acceptability of chemical use. It is based on predicted exposure levels, predicted no-effect levels of individual chemicals and politically defined degrees of acceptable risk. Each of these processes involves a series of value judgements and estimations. Risk assessment is therefore highly subjective. 

Safety Critical Actions—Specific steps humans take that provide layers of protection to lower the risk category of a specific scenario or scenarios from unacceptable to acceptable as defined by organizational risk tolerance criteria. Sometimes called administrative control. Such steps... 

The accepted risk is a risk inferior to a level defined in advance either by law, technical, economical, or ethical considerations. The risk analysis, as it will be described in the following sections, has essentially a technical orientation. The minimal requirement is that the process fulfils requirements by the local laws and that the risk analysis is carried out by an experienced team using recognized methods and risk-reducing measures that conform to the state of the art It is obvious that non-technical aspects may also be involved in the risk acceptation criteria. These aspects should also cover societal aspects, that is, a risk-benefit analysis should be performed... 

Acceptable risks or doses generally would be substantially higher than negligible levels used to define exempt waste. 

Establishing the boundaries in a risk-based waste classification system requires that one or more values of acceptable risk be specified. The values of acceptable risk are then used to establish the values of parameters that define the boundaries of the different waste classes. The process of establishing the value(s) of acceptable risk is part of risk management. Risk management is an essential aspect of establishing a waste classification system, but it has an important nontechnical component that reflects societal values. 

A proper reconciliation of the radiation and chemical paradigms for risk management is important to the development of a comprehensive and risk-based hazardous waste classification system. In particular, the proposed waste classification system developed in Sections 6.2 and 6.3 of this Report is based fundamentally on the concept that an acceptable risk generally can be substantially greater than a negligible risk. This distinction is used to define different classes of waste that pose an increasing hazard. 

The boundaries between different waste classes would be quantified in terms of limits on concentrations of hazardous substances using a quantity called the risk index, which is defined in Equation 6.1. The risk index essentially is the ratio of a calculated risk that arises from waste disposal to an allowable risk (a negligible or acceptable risk) appropriate to the waste class (disposal system) of concern. The risk index is developed taking into account the two types of hazardous substances of concern substances that cause stochastic responses and have a linear, nonthreshold dose-response relationship, and substances that cause deterministic responses and have a threshold dose-response relationship. The risk index for any substance can be expressed directly in terms of risk, but it is more convenient to use dose instead, especially in the case of substances that cause determinstic responses for which risk is a nonlinear function of dose and the risk at any dose below a nominal threshold is presumed to be zero. The risk index for mixtures of substances that cause stochastic or deterministic responses are given in Equations 6.4 and 6.5, respectively, and the simple rule for combining the two to obtain a composite risk index for all hazardous substances in waste is given in Equation 6.6 or 6.7 and illustrated in Equation 6.8. The risk (dose) that arises from waste disposal in the numerator of the risk index is calculated based on assumed scenarios for exposure of hypothetical... 

In its simplest form, risk assessment asks, How much exposure can we allow without causing irreparable harm Harm to whom Initially, to a maximally exposed individual and more recently to a sensitive and maximally exposed individual. For example, to keep chemical contamination to acceptable levels in a river, EPA would define acceptable risk to a maximally exposed individual. Acceptable risk would be defined as an exposure to a contaminant below its threshold for causing damage or, more often, a one-in-a-million risk of getting cancer from a... 

Risk characterization includes a comparison between toxicity values and/or exposure criteria and exposure (dose or media concentration) to determine whether the exposure is acceptable. US EPA developed a formalized system that is commonly used to determine whether chemicals are likely to present an unacceptable risk based on current and likely future use of the property. The estimated dose is used to calculate an additional lifetime cancer risk for each chemical regulated as a carcinogen. Typically, a total site risk (sum of the risk associated with all carcinogens identified at the site) is presented. Acceptable risk is defined by the agency, in the appropriate laws, or by regulations that govern the site. Acceptable risk is a function of policy or law but is supposed to be rooted in science. 

It is my hope that this book can define a very complex problem and describe solutions. The examples of dioxin cleanup issues and procedures are offered to provide engineers, health scientists, regulators, lawyers, business people, and other concerned individuals with a methodology applicable to other hazardous chemicals. I believe that science can detect pollutants in the environment and estimate their potential health risk. Society as a whole, scientist and nonscientist, determines acceptable risk. Society also plays a major role in managing risk because we face many problems and have limited resources to deal with them all. 

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